The color spectrum is an apt comparison. Yes, a single pure hue lies on a simple one dimensional wavelength scale. But a color sensed by your eyes is the result

The color spectrum is an apt comparison. Yes, a single pure hue lies on a simple one dimensional wavelength scale. But a color sensed by your eyes is the result of different intensities on three different receptor types, making the perceptual space more or less three dimensional. The color emitted by an object is even more complicated, with an intensity for each visible wavelength (to a first order approximation). Maybe the comparison should have been more explicit about how the one dimensional color spectrum is a drastically simplified representation of color physics, even though it already includes qualitatively distinct colors on a simple scale. On the other hand, while color has a lot of nuance to it, the total light energy emitted from a source might be a much simpler, totally scalar way to characterize light sources. If you squint hard, you can think of the autism spectrum concept as closer to intensity than to color.